* Added 2 ffat partition schemes for 4MB modules + improved descriptions.
Existing format options were unclear on how much spiffs you were
getting. Also add missing 1MB App/3MB Spiffs split.
This addresses https://github.com/espressif/arduino-esp32/issues/1799
This makes it very clear what each option gives you, and also adds 2 options
to get ffat on 4MB chips..
* Added link to ffat howto.
